I suspect the early clone award has to go to someone like Netronics R&D who
offered ISA-slotted mobo kits that did not feature graphics adapters of any
sort--output was intented to be RS232 to a terminal. I think I have some
circuit diagrams and literature from them in my files.
The first AT clone award candidate might be Faraday with their "A Tease"
mobo. Featured a 6 MHz 286, but with serial and parallel ports on the
mobo. I had one for a very long time before it developed serious problems.
I still have the circuit diagrams.
Cheers,
Chuck